The present invention relates to a sack or pouch for packing a material therein and to a laminate film for the sack, and more particularly, to the sack and the laminate film which is easily tearable yet having sufficient fracture strength and sealability.
The present invention also relates to a method for producing such sack or pouch and for producing the laminate film therefor.
A composite film is generally available as a material of a sack or pouch. The composite film includes a polyethylene film laminated on an ordinary cellophane sheet or paper. When the pouch or the sack formed of the laminated film is required to be opened, a heat-sealed portion of the pouch can be manually torn, i.e., a user can manurally break the seal at the heat-sealed portion. Therefore, such type of pouch is widely available. However, the composite film does not provide sufficient fracture strength and fluid-tightness particularly against moisture. Accordingly, a content to be packed is subjected to limination.
In order to overcome these drawbacks, a plastic laminated film is used as a material of the sack or pouch so as to improve fracture strength and moisture resistivity. However, the plastic laminated film provides relatively high tearing strength, so that it would be rather difficult to manually tear a pouch open at its sealing portion. Therefore, a cutter or other jig must be used to open the pouch.
In case of the pouch formed of the above-described plastic laminated film, demand has been made for manually open the pouch at its heat-sealed portion. To meet with the demand, V-shaped or I-shaped notch is formed at the heat-seal portion. Such notches serve to concentrate tearing force thereat and to propergate the force along the tearing direction.
Such notches can be easily formed by the lamination film manufacturer prior to filling a content in the package or pouch. However, if the film manufacturer simply supplies a rolled lamination film to the lamination film users, it would be rather difficult for the users to form such notch at the heat-sealed portion of the pouch during pouch production and content packing processes.
Japanese Patent Publication 61-39228 discloses a pouch 1 in which a heat-sealed portion 2 is subjected to a plurality of minute scoring or scratching 3 without formation of V-shaped notch as shown in FIG. 1. These scratches 3 are formed to a sheet prior to the production of the pouch, i.e., prior to the heat-seal process. Alternatively, after heat-seal process, these scratches are formed at the heat-sealed portion 2.
In this case, it would be rather difficult to form the scratches at a sheet web so as to correctly align the scored or scratched portion with the heat sealed portion in a subsequent heat-seal process. On the other hand, during heat-seal process, it would be also difficult and time-consuming to form scratches at the heat-sealed portion.